Following a canceled E3 unveiling, Halo 3: ODST was formally announced at the 2008 Tokyo Game Show by Microsoft and Bungie Studios. At the time, the game had been billed as complementing the overall Halo 3 experience. Speaking to Game Informer magazine last fall, Bungie design lead Joe Bertone described the game as "a three-to-five-hour expansion pack," with cinematic director Joe Staten adding that "we do not view this as a $60 title."

In a statement provided to GameSpot, Microsoft explained its pricing decision thusly: "At the time [of Bungie's comments], the overall scope of Halo 3: ODST was not yet finalized, and since then, the project has grown increasingly more ambitious. We believe this stand-alone experience is much more than just an expansion. Halo 3: ODST provides a new campaign from the point of view of an entirely new character. Combine that with three new multiplayer maps, the entirely new cooperative mode called Firefight [shown below], and the complete Halo 3 multiplayer collection on a stand-alone disc, we feel this is a good value and tremendous addition to the Halo franchise."

All editions of Halo 3: ODST, however, have two other incentives. Besides three exclusive multiplayer maps, the game disc will contain the levels from the Halo 3 Mythic Map Pack, released in April for MSP800 ($10). It will also contain an invitation to participate in the 2010 multiplayer beta of Halo: Reach, Bungie's mystery-shrouded next chapter in the Halo saga.